Fixation mechanism for an implant

ABSTRACT

An ankle prosthesis has a tibial component configured for attachment to a tibia of a person, and a talar component. The talar component has a first surface configured for facing the tibial component and a second surface configured for facing a talus of the person. The second surface has first and second arms attached to it, for pivoting or flexing outwardly in medial and lateral directions, respectively, to engage side surfaces of a previously formed slot in the talus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/100,695, which was filed on Jan. 7, 2015, the entirety ofwhich is herein incorporated by reference.

FIELD

This disclosure relates to medical devices generally, and morespecifically to an implant suitable for attachment to at least one bone.

BACKGROUND

Numerous ankle joint replacement prostheses have been developed.

U.S. Patent Application Publication No. 2014/0135939, assigned to theassignee of the present patent application, discloses an ankleprosthesis comprising: a tibial component configured for attachment to atibia, and a talar component configured for attachment to a talus. Thetibial component comprises an attachment surface on a proximal portionand an articulation surface on a distal portion. The talar componentcomprises an attachment surface on a distal portion and an articulationsurface on a proximal portion. The articulation surface of the tibialcomponent comprises at least one convex contour on a medial portion andat least one convex contour on a lateral portion. The articulationsurface of the talar component comprises at least one concave contour ona medial portion and at least one concave contour on a lateral portion,configured to compliment the articulation surface of the tibialcomponent. The articulation surface of the talar component comprises alip configured to maintain congruence of the articulation surface of thetibial component with the articulation surface of the talar component.

The talar component is attached to the talus by one or more screws orone or more rods.

SUMMARY

In some embodiments, an ankle prosthesis comprises a tibial componentconfigured for attachment to a tibia of a person, and a talar component.The talar component has a first surface configured for facing the tibialcomponent and a second surface configured for facing a talus of theperson. The second surface has first and second arms attached thereto,for pivoting or flexing outwardly in medial and lateral directions,respectively, to engage side surfaces of a previously formed slot in thetalus.

In some embodiments, a prosthesis comprises a first component configuredfor attachment to a first bone of a person, the first component havingan articulating surface. A second component has an articulating surfaceconfigured for facing the articulating surface of the first component,the second component has a second surface configured for facing a secondbone of the person. The second surface has first and second armsattached thereto, for pivoting or flexing outwardly in medial andlateral directions, respectively, to engage side surfaces of apreviously formed slot in the second bone.

In some embodiments, a method of fixing an implant component to a bone,comprises: forming a slot in the bone, the slot having side edges;positioning the implant component adjacent the bone, so that first andsecond arms of the implant component fit within the slot; and pivotingor flexing the first and second arms towards respective side edges ofthe slot.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an exemplary attachment plate suitablefor inclusion in a talar component of an ankle prosthesis according tosome embodiments.

FIG. 2 is a distal (bottom) plan view of the attachment plate of FIG. 1.

FIG. 3 is a cross-sectional view taken along section line 3-3 of FIG. 2.

FIG. 4 is a cross section of the talar component including theattachment plate of FIG. 1.

FIG. 5 is a distal (bottom) plan view of the attachment plate of FIG. 2,with its arms rotated.

FIG. 6 is a cross-sectional view taken along section line 6-6 of FIG. 5.

FIG. 7 is an anterior view of tibia and talus with the implantedprosthesis including the distal plate portion of FIG. 1.

FIG. 8 is a distal (bottom) plan view of a second embodiment of theattachment plate with its arms flexed.

FIG. 9 is a cross section of the attachment plate of FIG. 8.

FIG. 10 shows the slot of FIG. 4, as viewed from a proximal vantagepoint.

FIGS. 11A to 11C schematically show three alternative mountings of thearms relative to the cortical bone.

DETAILED DESCRIPTION

This description of the exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description, relativeterms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,”“below,” “up,” “down,” “top” and “bottom” as well as derivative thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should beconstrued to refer to the orientation as then described or as shown inthe drawing under discussion. These relative terms are for convenienceof description and do not require that the apparatus be constructed oroperated in a particular orientation. Terms concerning attachments,coupling and the like, such as “connected” and “interconnected,” referto a relationship wherein structures are secured or attached to oneanother either directly or indirectly through intervening structures, aswell as both movable or rigid attachments or relationships, unlessexpressly described otherwise.

This disclosure provides an ankle prosthesis having an attachment platefor fixing the talar component of the prosthesis to bone. The attachmentplate can provide stability, even in the case of compromised soft tissueor bone. Depending on the condition of the patient's bones, theattachment plate can be used to grip cancellous bone, the posteriorcortical wall, or both. In some patients, the plate may be used to gripthe medial and lateral cortices.

FIG. 1 is an isometric view of an exemplary attachment plate 100suitable for inclusion in a talar component 140 (FIG. 4) of an ankleprosthesis 150 (FIG. 7) according to some embodiments of thisdisclosure. FIG. 2 is a distal (bottom) plan view of the attachmentplate 100. FIG. 3 is a cross-sectional view taken along section line 3-3of FIG. 2. FIG. 4 is a cross section of the talar component 140including the attachment plate 100.

The ankle prosthesis 150 comprises a tibial component 160 (FIG. 7)configured for attachment to a tibia of a person, and a talar component140 configured for attachment to the talus 20. In some embodiments, thetalar component 140 approximates the natural anatomy of the talus boneand the tibial component comprises a complementary contour. In otherembodiments, the natural anatomy is mimicked in a reverse orientation,such that the tibial component 160 has a bicondylar contour and a talarcomponent 140 has a complementary contour. The tibial component 160 hasan attachment surface 13 and an articulating surface 15.

In some embodiments, the tibial component 160 is a unitary body formedof a single piece of material, such as titanium alloy, cobalt-chromealloy, chrome-titanium alloy or stainless steel. In other embodiments(not shown), the attachment surface 13 is formed on a proximal portionsuitable for permanent insertion and formed of a material such astitanium alloy, cobalt-chrome alloy, chrome-titanium alloy or stainlesssteel, and the articulating surface 15 is formed on a distal portionwhich is a detachable and replaceable insert mounted to the proximalportion. The distal portion can be made of a different material from theproximal portion. For example, the distal portion can be made of apolymer material, such as ultra-high molecular weight polyethylene(UHMWPE).

In some embodiments, the tibial component 160 is affixed to the distalend of the tibial bone by a stem 17, which can be a unitary stem or amodular stem (not shown) comprising two or more stem sections. In otherembodiments (not shown), the tibial component has a pair of expandablearms similar to the arms 104 of the tibial component 160 describedbelow.

A talar component 140 has a first surface (an articulating surface) 27configured for facing the tibial component 160 and a second surface (anattachment surface) 103 configured for facing a talus 20 of the person.The second surface 103 has first and second arms 104 attached thereto,for pivoting or flexing outwardly in medial and lateral directions 132,133 (FIG. 5), respectively, to engage side surfaces of a previouslyformed slot 21 (FIGS. 4 and 10) in the talus 20.

In some embodiments, each of the arms 104 is pivotally attached to thesecond (attachment) surface 103 of the talar component 140 by a pin 106.The arms 104 can be pivoted by a driving mechanism (described below) togrip cancellous bone, the posterior cortical wall, and/or medial andlateral cortical walls.

In some embodiments, the second (attachment) surface 103 is included ina distal plate portion 102 having first and second guide slots 112, andeach of the arms 104 has a pin 116 extending from the arm. The pin 116is movable within the guide slot 112 during pivoting or flexing of thearms 104.

In some embodiments, a driving mechanism 120 includes a separator 122positioned between the first and second arms 104. The separator 122 isconfigured to be advanced towards an anterior end of each of the firstand second arms 104 attached to the second (attachment) surface 103, forcausing the first and second arms 104 to pivot or flex outwardly, in themedial and lateral directions 132, 133, as best seen in FIG. 5. In someembodiments, the separator 122 is a cone or wedge.

In some embodiments, the separator 122 is attached to a threaded member124 for moving the separator in an anterior-posterior direction. Forexample, as shown in FIGS. 1, 2 and 5, an end of the threaded member 124can be fixedly attached to the separator 122. In some embodiments, theattachment is by engagement between the threaded member 124 and a femalethread (not shown) in separator 122. In other embodiments, the threadedmember 124 and separator 122 are two sections of a single unitary pieceformed (e.g., by casting) from a single material. In other embodiments,the threaded member 124 can have an end interference-fitted to theseparator 122.

The threaded member 124 is threadably received by a female socket 126fixedly attached to the second (attachment) surface 103. In someembodiments, the female socket 126 is formed from the same piece ofmaterial as the distal plate portion 102 and is spaced apart from theplate portion 102 by a rib or support member 127. The threaded member124 has a socket 128 or slot (not shown) at the anterior end of thethreaded member 124. The surgeon can rotate the threaded member 124using a tool 130 (FIG. 5) having a tip configured to be received by thesocket 128 or slot (not shown). When the surgeon rotates the threadedmember 124, the threaded member moves along the anterior-posterior axis109 of the implant 150. When the threaded member 124 moves in theanterior direction, the separator 122 also moves in the anteriordirection, causing the posterior ends of the arms 104 to pivot outwardin the medial and lateral directions 132, 133. (If the distal plateportion 102 is attached to the left talus, direction 132 is medial anddirection 133 is lateral. If the distal plate portion 102 is attachedthe right tibia, direction 132 is lateral and direction 133 is medial.)

In other embodiments (not shown), the separator 122 is a wedge havingstraight sides that are engaged by the medial sides of the arms 104,preventing the wedge from rotating. The threaded member 124 isthreadably received by the wedge, and can rotate relative to the wedge,causing the wedge 122 to advance or retract along the threaded member inthe anterior-posterior direction 109. The threaded member 124 can bemounted to permit rotation, but not linear travel. For example, thethreaded member can have a smooth section (not shown) that serves as ajournal of a journal bearing. The female socket 126 is replaced by asmooth socket or bearing (not shown) that receives the smooth section ofthe threaded member 124. The result of rotating the threaded member isthe same as described above; the separator 122 advances, causing theposterior ends of the arms 104 to separate from each other in themedial-lateral direction 132, 133.

FIG. 6 is a cross-sectional view of the talar component 140 after thearms 104 are pivoted outwardly in the medial and lateral directions.Compared to the cross-sectional views in FIGS. 3 and 4 (prior topivoting the arms 104), FIG. 6 shows the rear of each arm 104 extendingoutwardly to grip the medial and lateral sides of the slot 21.

In some embodiments, each of the arms 104 has a plurality of barbs 110on an outer (medial or lateral) edge of the arm. The barbs 110 can gripcancellous bone or the cortical walls of the bone.

In some embodiments, the slot 21 is formed in the talus 20 with undercutside surfaces, in a trapezoidal or dove-tail shape, and the arms 104have a medial-lateral dimension DML (FIG. 3) that increases from aproximal side 104 p of each arm 104 adjacent the second surface 103 to adistal side 104 d of each arm 104 configured to face the talus 20. Insome embodiments, each arm 104 has an approximately trapezoidal crosssection, as shown in FIGS. 3, 4 and 6. The two arms 104 havingapproximately trapezoidal cross sections are adapted to be received inthe dove-tail shaped slot 21 in the talus 20. The outer sides of thearms 104 bear against the side walls of the slot 21. The wider distalsides 104 d of the arms extend under the undercut side walls of the slot21, resisting pullout.

In some embodiments, the distal plate portion 102 has an anterior lip108. The implant 150 is configured to be inserted from an anterior side.The anterior lip 108 provides a positive stop that bears against theanterior cortical wall of the talus when the distal plate portion 102 isinserted in the posterior direction. When the arms 104 pivot outwardly,the outside of each arm applies a force in an oblique direction. Theforce has a component in the medial-lateral direction and a component inthe anterior direction. As the angle θ (FIG. 5) of the pivotingincreases, the anterior component of the force applied by each arm alsoincreases. The anterior component of the force is approximatelyproportional to the sine of the pivot angle θ. This anterior componentof the force is met by an equal and opposite posterior force between theanterior lip 108 and the anterior cortical wall. Thus, the plate portion102 provides additional clamping forces in the anterior-posteriordirection. In some embodiments, the anterior lip 108 has an aperture(not shown) to permit access to the socket 128 of the threaded memberthrough the aperture while the anterior lip abuts the talar bone 20.

In some embodiments, the talar component 140 comprises a proximalportion 19 and a distal plate portion 102 made of different materialsfrom each other. For example, the proximal portion 19 having thearticulating surface 27 can be a replaceable component made of amaterial such as UHMWPE. The distal plate portion 102 can be made of amaterial such as titanium alloy, cobalt-chrome alloy, chrome-titaniumalloy or stainless steel or the like, for permanent implantation. Insome embodiments, as shown in FIG. 4, the distal plate portion 102 has adovetail-shaped slot 114 for receiving a trapezoidal member 28 of theproximal portion 19, forming a dovetail joint between the proximalportion 19 and the distal plate portion 102. This allows replacement ofthe proximal portion 19 having the articulating surface 27 (e.g.,following wear of the articulating surface 27, or to make an adjustment)through the anterior side of the patient's ankle.

In some embodiments, the bottom surface of the implant 150 or arms 104are coated to enhance biologic fixation (e.g., porous coated or plasmasprayed).

To insert the implant, the surgeon fixes the patient's foot in asuitable foot holder, and supports the posterior side of the calf. Thesurgeon makes an incision on the anterior side and performs soft tissueand ligament release as appropriate. The tibia and calcaneus are fixedusing rods and/or wires. Approximately 6-8 mm is cut from the proximalend of the talus, providing a flat surface for attaching the talarcomponent 140. The distal end of the tibia is cut to provide areceptacle for the proximal end 13 of the tibial component 160. A holeis drilled in the cut surface to receive the tibial stem 17 of thetibial component 160.

The surgeon forms the slot 21 (as shown in FIG. 10) in the resectionedproximal surface of the talus 20. The slot 21 can be formed using athree-sided punch, a saw with a guide having three slots, or a dovetailstyled end mill. The side walls 21 s of the slot 21 are undercut, asshown in FIG. 4, so as the arms 104 are actuated outwardly, the plateportion 102 is drawn down onto the resected surface of the talus 20. Inaddition, the side walls 21 s of the slot 21 are not parallel to eachother. As best seen in FIG. 10, the slot 21 has the general shape of anisosceles trapezoid when viewed from a vantage point that is proximalrelative to the talus 20. The posterior side (based) of the slot 21 iswider than the anterior side, to prevent the plate portion 102 fromtranslating back in the anterior direction once the arms 104 are drivenapart by the driving mechanism. This trapezoidal shape provides room forthe arms 104 to pivot or flex outwardly before engaging the side walls21 s of the slot 21. The side walls 21 s of the slot 21 are symmetricalabout the anterior-posterior axis 109.

In some embodiments, the surgeon removes a small amount of the bone onthe anterior side, to receive the anterior lip 108, so that the anteriorlip seats flush with the bone. In other embodiments, the anterior lip108 seats outside of the bone.

Depending on the quality of the talar bone, the slot 21 can bepositioned in different locations relative to the cortical walls, andthe length and pivot angle θ of the arms 104 correspondingly adjusted.For example, FIG. 11A shows the distal plate portion 102 positioned sothat the arms 104 are completely surrounded by cancellous bone, and donot touch the cortical walls. A corresponding slot 21 is formed in thetalus 20. (The size of the plate portion 102 is exaggerated for ease ofviewing, but in practice the corners of the plate portion 102 will notstick out from the talus as shown in FIG. 11A.) A configuration in whichthe arms 104 only contact cancellous bone may be suitable if thecancellous bone is of good quality (i.e., not excessively soft ordiseased).

FIG. 11B shows another configuration in which the length of the arms 104and the excursion (i.e., pivot angle θ of the arms 104) are selected sothat the posterior ends of the arms 104 abut the posterior cortical wallfor greater stabilization. A corresponding slot 21 is formed in thetalus 20. Such a configuration may be used when the cancellous bone isof lower quality.

FIG. 11C shows another configuration in which the length of the arms 104and the excursion (i.e., pivot angle θ of the arms 104) are selected sothat the anterior and posterior ends of the arms 104 abut the anteriorand posterior cortical walls, respectively, for still greaterstabilization. A corresponding slot 21 is formed in the talus 20.

The tibial stem 17 and the tibial component 160 are installed. Then thedistal plate portion 102 of the talar component 140 is inserted into theincision until the anterior lip 108 abuts the anterior cortical wall ofthe talus 20. The talar component 140 is positioned adjacent the bone20, so that first and second arms 104 of the talar component fit withinthe slot 21.

The two arms 104 are seated in the slot 21, and the surgeon uses thetool 130 to rotate the threaded member 124, to advance the separator 122in the anterior direction. The advancing of the separator causes the twoarms 104 to pivot outwardly about the pins 106 to expand in the medialand lateral directions. The surgeon continues to advance the separatoruntil the arms 104 grip the bone 20.

FIGS. 8 and 9 show a second embodiment of the attachment plate, in whicheach of the arms 204 is fixedly attached at one end (e.g., the anteriorend) to the second (attachment) surface 203 of the talar component 140by an integral post 205 joining each respective arm 204 to the secondsurface. In some embodiments, the integral posts 205 can be unitaryposts formed of the same piece of material as the arms 204. The postscan have the same shape as the pins 106, but do not pivot. Thus, theanterior ends of each arm 204 are constrained. When the separator 122 isadvanced in the anterior direction, the arms 204 flex in the medial andlateral directions, as shown in FIG. 8. The plate 202, arms 204 andposts 205 can be formed from a single piece of material by casting, forexample.

In some embodiments, the amount of flexing of the arms 204 is small, sothat the curved tracks 112 and guides 116 of the attachment plate 100are omitted.

In another embodiment (not shown), instead of a unitary post 205, theanterior end of each arm 204 can be fixed to the plate portion 202 withtwo or more fasteners (e.g., screws), for greater strength. The arms 204attached by fasteners can flex in the same manner shown in FIG. 8.

Although the operation of the pivoting arms 104 and the flexing arms 204is similar, the pivoting arms can provide a greater expansion in themedial-lateral direction. The flexing arms 204 of FIGS. 8 and 9 can beused where less expansion is suitable, such as for hard bones, such asbones of osteoarthritis patients. The flexing arms 204 of FIGS. 8 and 9may also be used where the arms can provide bi-cortical gripping. Thepivoting arms of FIGS. 1-7 provide greater expansion, and may besuitable for softer bones, such as bones of rheumatoid arthriticpatients.

Although the examples have been describe d with respect to use in thetalar component 140 of an ankle prosthesis 150, the attachment mechanismand method described herein can be used for other implants. For example,the attachment mechanism and method can be used for the tibial component160 of the ankle prosthesis 150. The plate portion 102 (or 202) can beoriented with the arms 104 (204) facing in the proximal direction,towards the tibia. A trapezoidal slot with undercut sides is formed in aresectioned distal surface of the tibia. The plate portion 102 (or 202)is attached to the tibia in the same manner described above withreference to attachment to the talus. In some embodiments, the tibialcomponent is unitary, and further includes an articulating surface. Inother embodiments, a distal portion of the tibial component having anarticulating surface can be attached to the distal side of the plateportion 102 (or 202), to complete the tibial component.

Thus, in some embodiments, a prosthesis includes a first component 160configured for attachment to a first bone of a person, the firstcomponent having an articulating surface 15; and a second component 140having an articulating surface 27 configured for facing the articulatingsurface 15 of the first component 140. The second component 140 has asecond surface 103 configured for facing a second bone of the person.The second surface 103 has first and second arms 104 attached thereto,for pivoting or flexing outwardly in medial and lateral directions,respectively, to engage side surfaces of a previously formed slot 21 inthe second bone. The pivoting or flexing is in a plane parallel to thesecond surface 103.

Although the subject matter has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed broadly, to include other variants and embodiments,which may be made by those skilled in the art.

1-20. (canceled)
 21. A method of fixing an implant component to a bone,comprising: forming a slot in the bone, the slot having side edges;positioning the implant component adjacent the bone, so that first andsecond arms of the implant component fit within the slot; and pivotingor flexing the first and second arms towards respective side edges ofthe slot.
 22. The method of claim 21, wherein the step of pivoting orflexing comprises advancing a wedge or cone between an end of the firstarm and an adjacent end of the second arm.
 23. The method of claim 22,wherein the step of advancing the wedge or cone includes rotating athreaded member attached to the wedge or cone.
 24. The method of claim21, wherein the slot is formed with an undercut, and each of the armshas a medial-lateral dimension that increases from a proximal side ofeach arm adjacent the second surface to a distal side of each armopposite the proximal side thereof.
 25. The method of claim 21, wherein:the slot is formed in cancellous bone, a respective lateral edge of eacharm has a plurality of barbs, and the pivoting or flexing step drivesthe barbs into the cancellous bone.